1. Field f the Invention
The present invention relates to a centrally controlled telecommunication switching system. It includes means adapted to establish and release call connections between inputs and outputs of a switching network under the control of at least two processors. Each processor in the system has access to a memory storing status words containing information about call connections established through said switching network and indicating the phase of these call connections, e.g. whether they are in the communication phase or not. Each processor, upon the occurrence of a breakdown of at least one other processor, executes a recovery program which consists in reading the information respecting phase stored in said status words and in releasing the corresponding call connections which are not in the communication phase.
2. Description of the Prior Art
Such a processor controlled telecommunication switching switching system is known from Belgian Pat. No. 709,719 (S. KOBUS et al 19-4-1-2-13) corresponding to U.S. Pat. No. 3,557,315, which issued on Mar. 10, 1970. Therein the mentioned recovery program is executed by a correctly operating processor upon one of the other processors becoming faulty and being put out of service. The status words read by the correctly operating processor are those storing information received from the faulty processor prior to becoming faulty and relating to call connections normally handled by this faulty processor.
The advantage provided by the execution of the above described program is that all the call connections which are in the communication phase are maintained. But a disadvantage is that some call connections are maintained even though the information thereof stored in the corresponding status words of the correctly operating processor might be faulty since they have been received from the processor which has now become faulty. This erroneous information may be the source of errors in the now correctly operating processor and lead to a breakdown of this processor.